[VIPS] Ideotype question (fwd)

'Toby' H D Bradshaw toby at u.washington.edu
Thu Oct 12 13:49:59 EST 1995


Forwarded from Tom Hinckley, University of Washington

-Toby Bradshaw
toby at u.washington.edu

---------- Forwarded message ----------
Date: Fri, 6 Oct 1995 15:42:03 -0700 (PDT)
From: T. Hinckley <hinckley at u.washington.edu>
Subject: Re: Light interception vs. total net photosynthesis

On Thu, 5 Oct 1995, 'Toby' H D Bradshaw wrote:

> It seems to me that APAR vs. productivity correlations *are*
> mechanistic, in that energy must be captured for photosythesis
> to occur

About as mechanistic as a diagram with genetics on the left and 
environment on the right coming together in a process box and producing 
growth and survival as an outcome

I mentioned a figure in Larcher. I was wrong, it actually is a figure 
from Coleman et al. (1995. Tree Physiology) where one axis is biomass 
(y) and the other is canopy photosynthesis (x and one step better than 
APAR).  Although Mark claims a linear relationship between canopy 
photosynthesis and biomass, I found that year and ozone exposure had a 
great impact on the slope and intercept of the various lines.  These 
data suggest that one needs, therefore, a different beta 0 and beta 1 
value for each clone and for each year (and may be for clone by ozone 
by year interactions).  A rough line gets you clearly in the ball park, 
however, if you wanted to select between the sensitive and resistant 
clones or understand what one clone had more root growth than another 
for equal photosynthesis, such diagrams would fail you.

.  As you point out, 
though, there are a lot of 
downstream > processes beyond light capture, and a lot of developmental
> changes that may affect the slope of the correlation as the stand matures.
> 
> Would you argue that, in "real life" based on what we now know, that
> a "practical" breeder would be better off measuring growth itself 
> rather than attempt to select for the morphological or physiological 
> sub-components of productivity?

I would agree with this.  The only reason to go to finer levels is to 
capture things not found in biomass or to understand one clone A in one 
environment does well, but in other not.

Tom




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